By KATIE ZEZIMA


FALL RIVER, Massachusetts - During 34 years of smoking, Carolyn Smeaton has tried countless ways to reduce her three-pack-a-day habit, including a nicotine patch, nicotine gum and a prescription drug. But stop-smoking aids always failed.

Then Ms.Smeaton tried an electronic cigarette, which claimed to be a less dangerous way to feed her addiction. The battery-powered device she bought online delivered an odorless dose of nicotine and flavoring without cigarette tar or additives, and produced a vapor mist nearly identical in appearance to tobacco smoke.

“I feel like this could save my life,” said Ms.Smeaton, 47, who has cut her tobacco smoking to a pack and a half daily, supplemented by her ecigarette.

That electronic cigarettes are virtually unstudied has not deterred thousands of smokers from flocking to malls and the Internet to buy them. And because they produce no smoke, they can be used in workplaces, restaurants and airports.

The reaction of medical authorities and antismoking groups has ranged from calls for testing to skepticism to outright hostility. Opponents say the safety claims are more rumor than anything else, since the components of e-cigarettes have never been tested for safety.

For $100 to $150 or so, a user can buy a starter kit including a batterypowered cigarette and replaceable cartridges that typically contain nicotine (though cartridges can be bought without it), flavoring and propylene glycol, a liquid whose vaporizing produces the smokelike mist. When a user inhales, a sensor heats the cartridge. The flavorings include tobacco, menthol and cherry, and the levels of nicotine vary by cartridge.

Propylene glycol is used in antifreeze, and also to create artificial smoke or fog in theatrical productions. The Food and Drug Administration has classified it as an additive that is “generally recognized as safe” for use in food. But when asked whether inhaling it was safe, Dr.Richard D.Hurt, director of the Nicotine Dependence Center at the Mayo Clinic, said, “I don’t think so, but I’m not sure anyone knows for sure.”

Of the e-cigarettes themselves, Dr.Hurt added: “We basically don’t know anything about them. They’ve never been tested for safety or efficacy to help people stop smoking.”

Sales and use of electronic cigarettes are already illegal on safety grounds in Australia and Hong Kong, and some other countries regulate them as medicinal devices or forbid their advertising. So far the United States has focused only on stopping them at the border, although Senator Frank R.Lautenberg has asked the F.D.A. to take them off the market until they can be tested.